The original inspiration for this circuit was a vague concept of an amateur radio phone patch. These devices are normally of the "push to talk" or "voice operated exchange" (VOX) type due to the one way at a time nature of two way radio communication. Also known was of the existance of telephone "hook ups" used in commercial radio and television broadcast stations. Although the principal of both of these types of couplers was known my device was not patterned intentionally off either.
In the prior art are numerous examples of telephone amplifying systems. Most commercially available "speakerphones" are of the VOX simplex (single channel at a time) type which thwart the natural simultaneous two way characteristic of the telephone medium. The reason for this is that most speaderphones have the microphone and speaker built into the same cabinet housing which would cause a feedback problem if operated as a duplex (simultaneous two way) system. Many patents in the prior art provide improvements to the basic telephone amplifier scheme primarily in the realm of feedback suppression by means of automatic volume control (signal comparison) circuitry. My design rejects the necessity of feedback suppression circuitry relying on the user's discretion with regard to microphone and speaker proximity to sucessfully avoid feedback.
The prior art shows that it has long been understood that two amplifiers could be used to amplify the incoming and outgoing signals of a telephone. It is not my intention, therefore, to proclaim as novel the well known fact that a stereo amplifier is two amplifiers, rather that a stereo being two amplifiers is particularly suited to amplify the telephone composite signal. To clarify by reference to the prior art, Snopko (U.S. Pat. No. 4,338,492) reveals not that a television contains an audio amplifier but rather that it can be used to amplify a telephone and contributes a unique circuit design to interface the telephone and the television.
If a home entertainment variety stereo amplifier used as a speakerphone can be distinguished from speakerphones designed primarily for that purpose then the invention is the combination of the telephone, stereo, speakers, mixer, signal sources (microphone etc.) and the interconnecting apparatus rather than just the interconnecting apparatus. The claims are therefore framed to express that viewpoint.
The idea came as a result of my telephone and my stereo being physically next to each other. I thought, "I wonder what would happen if I connect these wires to this?" Consequently I discovered the astonishingly natural suitability of a stereo amplifier for use as a speakerphone and its potential in the realm of music. With this device it is possible to play music by telephone. One can put a band together by conference call for jam sessions, rehearsal, recording, auditions, and live broadcast over radio and television.